A skin of a fuselage of an aircraft is constructed of a thin member called a skin panel (for example, refer to Patent Document 1). In recent years, a technology for integrally forming a broader skin panel than before with using fiber-reinforced resin composite materials (hereinafter, simply referred to as “composite materials”) has been developed. For example, even though a skin panel in the vicinity of the center of the fuselage of a large aircraft has a cylindrical shape, the technology integrally forms a seamless skin panel of a cylindrical shape.
In order to manufacture the skin panel of a cylindrical shape described above, prepreg is laminated onto an outside surface of a cylindrical core die (generally called a “mandrel”), and the laminated prepreg (hereinafter, referred to as a “laminate”) has a cylindrical shape overall. “Prepreg” is a sheet-shaped material prepared by impregnating a textile such as carbon fiber, or a unidirectional material including carbon fiber and the like with a semi-cured thermosetting resin (epoxy resin, etc.). Then, the laminate is put under pressure and heat to be cured. At the time of curing, a plate-like surface die (generally called a “curl plate”) which has a smooth surface is brought into tight contact with the surface of the laminate so that the smooth surface of the surface die will be transferred, molding the skin panel with a smooth surface. The surface is smoothed for the reason that the outside surface of the skin panel comes into contact with an air current, and high smoothness is required.
However, since the skin panel of a large aircraft has a considerably large diameter of 5 to 10 m, it is substantially impossible to perform molding with a single surface die. Therefore, actually, a plurality of partial surface dies having an inner surface of a circular-arc sectional shape (i.e., the shape of a partial circle in section) is assembled to construct a mold. However, in the case of constructing a mold with a plurality of partial surface dies, since a thermosetting resin temporarily exhibits a viscosity drop due to the heat at the time of curing a laminate, there is a problem that an edge of the partial surface die is pressed against the laminate, thereby intruding into the laminate.
As a measure for this problem, a method of using a connecting member (generally called a “pre-cured strip”) which is a composite material cured in advance is proposed. That is, as shown in FIG. 3A, a connecting member 203 is inserted between a partial surface die 201 and a laminate 202 so as to correspond to a joint between the partial surface dies 201, and is then put under pressure and heat so as to be cured. Through this method, as shown in FIG. 3B, since the connecting member 203 intrudes into the laminate 202, a portion corresponding to the joint between the partial surface dies 201 is smoothed. In this case, since the connecting member 203 is cured in advance and is rigid, the partial surface die 201 does not intrude into the connecting member 203.